Polymer (plastic) materials have found their way into virtually every manufacturing sector. The ubiquity and abundance of these materials requires careful attention be paid to their flammability properties, especially for applications involving transportation, building materials, consumer goods, and electronics. As most polymeric materials are inherently flammable in their native state, additives are typically blended into polymeric materials to reduce their flammability.
Brominated organic compounds are commonly used as additives for retarding and slowing the flammability of plastic compounds they are blended with. They may be blended alone or in combination with other brominated or non-brominated flame retardants in a synergistic manner. Optionally, additional compounds may be added to the blend in order to achieve good flame-retarding results and maintain durability. In general brominated aliphatic compounds are more effective flame retardants than brominated aromatic compounds since they tend to break down more easily [International Plastics Flammability Handbook, 2nd edition, Jurgen Troitzsch, p. 45]. However, brominated aromatic compounds are often more stable than the aliphatic bromides, therefore they discolor less readily.
A flame-retardant widely used in polyolefins and other plastics is tetrabromobisphenol A [International Plastics Flammability Handbook, 2nd edition, Jurgen Troitzsch, p. 56] but it suffers from heavy blooming and has limited UV (ultraviolet radiation) stability. By “blooming” it is meant that a separation of the additive from the polymer matrix occurs, which has a negative effect on the surface appearance of the plastic articles. Many of the above mentioned flame-retardants require the additional use of a synergist such as antimony oxide, or else their activity as flame retardants is greatly diminished.
Bisphenol C (BPC) (1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene) has been shown by many research groups to serve as a flame retardant and blendable additive as well as a monomer for producing flame retardant polymer materials [J. R. Stewart, “Synthesis and Characterization of Chlorinated Bisphenol-Based Polymers and Polycarbodiimides as Inherently Fire-Safe Polymers,” University of Massachusetts: Ahmerst, Mass., (2000); J. L. Jurs, et al, SAMPE International Symposium, 1244 (2000); Lyon, R. In International Aircraft Fire and Cabin Safety Research Conference; Atlantic City, N.J., (2001); J. L. Jurs, J. M. Tour, Polymer, 44, 3709 (2003)]. When BPC decomposes thermally, it releases HCl gas as well as forming a polycyclic aromatic decomposition product that serves as a char layer. This unique ability to fight the flame front in both the gas phase and condensed phase is helpful in creating materials with excellent fire resistance properties [Lyon, R. In International Aircraft Fire and Cabin Safety Research Conference; Atlantic City, N.J., (2001); S. I. Stoliariv, et al, Polymer, 43, 5463 (2002)].
Most flame retardant polymers are highly rigid structures containing large amounts of aromatic char-forming functionality. These polymers tend to be hard to process and have high melting temperatures, resulting in elevated cost and rigorous processing requirements. The incorporation of flexible linkers for making processable polymers, an approach commonly used in making vinyl addition polymers, has not been considered a viable approach to making flame retardant polymers since the flexible linkers tend not to be flame resistant. Polymers made using BPC-based chain growth systems, however, could contain both the flexibility of a vinyl backbone and the fire resistance qualities inherent in BPC. Such polymers could overcome the processing difficulties of other BPC polymers, while still retaining their ability to rate as V-0 as tested by UL-94 standards (Underwriters Laboratories).